<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body></body>
  <script>
    let obj = {
      [Symbol.toPrimitive]() {
        return 200;
      },
      valueOf() {
        return 300;
      },
      toString() {
        return 'Hello';
      },
    };
    console.log(obj + 200);//400
  </script>
</html>
